This invention relates to an optical pickup head for optically reproducing, recording, or erasing information from or on an optical or magneto-optical recording medium.
An optical recording medium such as an optical disk is formed with a pattern of a groove or pits which represents recorded information. Some optical pickup heads are used in reproducing information from such an optical recording medium. In general, the optical pickup head applies a laser light beam to the optical recording medium and detects the laser light beam reflected back from the optical recording medium. Since the reflected laser light beam depends on a pattern on the optical recording medium, the reflected laser light beam represents information on the optical recording medium. Thus, the detection of the reflected laser light beam enables the reproduction of the information.
Japanese published unexamined patent application 1-273238 discloses an optical pickup head. As will be described later, the optical pickup head of Japanese application 1-273238 has some problem.
U.S. Pat. No. 4,929,823 discloses an optical pickup head which has a holographic optical element disposed in an optical path among a light source, an optical recording medium, and a photodetector unit. The holographic optical element serves to generate reliable focusing and tracking error signals.